We now consider the case of tetraquarks with two heavy quarks and two heavy antiquarks.
There is a flurry of calculations, in particular following the announcement by LHCb of the peak in the \(J/\psi \) -\(J/\psi \)  distribution, and its interpretation as a \(cc\bar{c}\bar{c}\)  resonance.
One of the questions raised by the LHCb discovery is whether there exist bound states of \(cc\bar{c}\bar{c}\)  or \(bb\bar{b}\bar{b}\) .
Most of calculations are done in a simplified scheme with a diquark and an antidiquark. As shown elsewhere [1]}, this is not a good approximation to the standard quark model,Of course, if the diquark is introduced in the formulation of the theory, we are not dealing with an approximation but with an alternative model, subject to others pros and cons. and hence we do not include the corresponding papers in our discussion.
Using a standard (color-dependent, pairwise) potential and an expansion on an harmonic-oscillator basis, Llyod and Vary [2]} found a bound \(cc\bar{c}\bar{c}\)  bound state, but their result was not confirmed by other authors.In our opinion, this is due to their use of an individual-particle basis and a cumbersome subtraction of the center of mass energy. In [1]}, [4]} and references therein, an explanation is given on why in the chromoelectric limit \(QQ\bar{Q}\bar{Q}\)  is not bound, while the electric analog \(e^+e^+e^-e^-\)  is stable against dissociation into two \(e^+e^-\)  atoms.
